Human joints can become damaged as a result of accident or illness. Such damage can be, for example, to the articular cartilage covering the ends of the bones at the joint as well as the intra-articular cartilage between the ends of the adjacent bones of the joint. When the damage to the joint is severe, a joint endoprosthesis can be implanted to improve the comfort and mobility of the patient.
Joint endoprostheses have been developed to replace native tissue of several human joints. There are a variety of knee prostheses, hip prostheses, shoulder prostheses, ankle prostheses and wrist prostheses available to relieve patient suffering. Such devices are available, for example, from the assignee of the present invention, DePuy Orthopaedics, Inc. of Warsaw, Ind.
Standard joint endoprostheses include metal components that are affixed to the articulating ends of the bones of the joint and commonly include a bearing component positioned between the metal components. Standard bearing components of joint endoprostheses have a surface against which one of the metal components articulates. For example, hip endoprostheses include a metal femoral component to be affixed to the proximal femur and a metal cup to be affixed to the acetabulum. Many of these standard hip endoprostheses include a liner in the acetabular cup against which the femoral component articulates. Knee prostheses commonly include a femoral component to be affixed to the distal femur and a tibial component to be affixed to the proximal tibia. Bearings are typically between the femoral and tibial components. Similar systems with bearings are available to replace other joints in the body.
Standard bearings for joint endoprostheses are made of ultrahigh molecular weight polyethylene (UHMWPE), ceramic and metal. Bearing wear is problematic in the orthopaedic field. Several patents have addressed the problem particles produced by UHMWPE wear, and the association of these particles with osteolysis. See, for example: U.S. Pat. No. 6,281,264, “Chemically crosslinked ultrahigh molecular weight polyethylene for artificial human joints” and U.S. Pat. No. 6,228,900 “Crosslinking of polyethylene for low wear using radiation and thermal treatments.”
Undue bearing wear can result in conditions requiring that the joint endoprosthesis be removed and replaced in a revision procedure. Accordingly, early detection of bearing wear could find use as a signal to the orthopaedic surgeon that some type of intervention is needed before the condition degenerates to the point of requiring revision surgery. For example, the surgeon may determine that the patient needs to make some lifestyle changes if revision is to be postponed. Moreover, if therapeutic agents to treat early stage osteolysis are available, these agents could be administered before the condition degenerates to the point where revision surgery is necessary.